1. Field of the Invention
This invention relates to improvements in a compact, large aperture ratio, long focus lens of a short total length having an angle of view of 28.5.degree. and an aperture ratio of 1.4.
2. Description of the Prior Art
As a lens of such type, there is known the lens of U.S. Pat. No. 3,948,584 (Japanese Laid-open Patent Application No. 8527/1975) which uses a so-called modified Gauss type lens. This lens has a short back focal length and is compact for its long focal length, but in order to shorten the back focal length, the refractive power of the forward lens group disposed forwardly of the diaphragm has been made substantially stronger than the refractive power of the rearward lens group disposed rearwardly of the diaphragm and although this lens has a quite large aperture ratio, i.e., F-number 1.4, its imaging performance has been insufficient. That is, the allotment of aberrations to the positive lens group forming the forward group has been great and therefore, correction of annular spherical aberration has been insufficient, and the increased refractive power of the negative lens group forming the forward group has caused extreme over-correction of spherical aberration, particularly, spherical aberration for the short wavelength light in the vicinity of g-line (.lambda.=436 nm), and thus the performance under open conditions has not been sufficient.